Just to add to this, the news story is far from the reality and the statement given by Specialist Auctions is quite misleading in the fact that it suggests that BOCN monitor whats for sale, which is not the case. I've copied and pasted a quote from Specialists Auctions statement and part of a message I got from BOCN's admin below.
"'We also have specialists from the British Ordnance Collectors Association who monitor what is being listed for sale." - Specialist Auctions
"I am not happy with the misleading statement allegedly made by specialist auctions to the press, it implys BOCN has specialists who monitor whats on their site.
This could be mis-interpretted as its our fault, passing blame for any possible mishaps onto us. We do not monitor any websites, we are not an officialy recognised organisation, we are a specialist collectors website. We are not associated in any way with spec auctions or any other sites." - BOCN Admin
Regarding whether the device in question was explosive or not, the seller of it (also a member of BOCN) has said that he had completely stripped the mortar bomb down and photographed it. He was sure that there was nothing dangerous about it. I personally think that it was something else that exploded and the mortar bomb got the blame either out of confusion, or to cover up the fact the kid had something he shouldnt have such as something he picked up on an MOD training area whilst on exercise with the ATC.